Plunger dies



March 26 1963 J. F. H. cusTl-:Rs ETAL 3,082,477

PLUNGER DIES Filed NOV. '7, 1960 3,982,477 PLUNGER BEES .lan F. H.Custers, Henry E. Dyer, Bernard W. Senior, and Peter T. Wedepohl, all ci.Iohannesburg Transvaal, Republic of South Africa, assignors to AdamantLaberatories (Proprietary) Limited, .lohannesburg Transvaal, Repubiic ciSouth Africa Filed Nov. 7, 1960, Ser. No. 67,73@ Claims priority',appiication Republic of South Africa Nov. it?, i959 Claims. (Cl..iS-16.5)

This invention relates to the production of a die capable of exertingpressures on material enclosed within its pressure chamber of the orderof say 50,000 atmospheres and above. While 4it is not excluded that thedie be used to compress the material in the cold, the purpose for whichthe die of the invention has been evolved is to compress the charge andheat it to elevated temperature simultaneously, so that the object ofthe invention is also to provide a die which can successfully be appliedto this end.

The production of dies which are capable of imposing on the materialcharged into them high pressures of the order of 50,000 .atmospheres andabove presents no great technical difficulties. Indeed, in laboratoryequipment dies have been made in which pressures -above 70,000atmospheres have been achieved. Similarly, there is no diiiiculty inbringing material to elevated temperature, say up to 1800 C. and thiscan readily be achieved while the material is kept under moderatepressure. Where, however, grave difficulties do arise is when materialis to be heated to temperatures of this order and simultaneouslymaintained under high pressure of the order of say 70,000 atmospheres.

The kind of die to which the invention relates is that in which aplunger is caused to enter the chamber to compress the charge against ananvi-l which is rigid or is a second plunger.

The limitation of this kind of die is the compressive strength of theplunger itself since the opposed axial forces upon it tend to spread itlaterally, or in the case of a brittle hard metal plunger, to causeplunger breakage. According to the inventoon, the die has a bodydeiining a pressure chamber, at least one plunger movable to enter thechamber to compress a charge within it, and supporting means for thatpart of the plunger protruding from the die consisting in a collarsurrounding that protruding part, located to be compressed between thebody of the die and the platen of the press containing the die, and makeof a material that undergoes plastic deformation at the pressure to beapplied to the die. The material is characterized by having mechanicalstrength properties such that it is capable of exerting a sustainedinward quasi-hydrostatic pressure on the plunger periphery of the orderof thousands of atmospheres.

If the material be a metal it is desirable that its yield shear strengthbe of the order of l() kilogrammes per square millimetre or greater;that its percentage elongation at tensile failure be of the order of 10%or more; and that it be characterized by the ability to increase itsyield shear strength by work-hardening as plastic deformation proceeds.

If the material be non-metallic it is desirable that it have a highinternal friction and low yield shear strength, so that it may resistthe tendency to extrude readily when compressed and so relieve theinward quasi-hydrostatic pressure generated.

It is not necessary that these mechanical properties of the collarmaterial obtain at room temperature for the collar may be heated to atemperature within a limited ata. i

3,032,477, Patented Mar. 26, i953 temperature range where the desiredmechanical properties obtain. f

The shape of the plunger may vary widely. It is desirable .although notessential that the outer face of the plunger in contact with the anvilbe of greater area than the inner face in contact with the charge, sotha-t the unit applied stress on the upper face is less than thatdeveloped in the lower face.

The radial inward support pressure may or may not be uniform over theperipheral surface of the plunger. It is desirable that this supportpressure be relatively high where the plunger enters the pressurechamber.

If part of the plunger encased in the collar have a cross-sectional areawhich increases toward the outer face, it may be, depending upon therate of increase` of area with distance from the inner face of theplunger, that the supporting stress, due to the collar, on the peripheryof the plunger at or near the inner plunger face may be insufficientlyenhanced as the plunger is forced through the coliar to enter thepressure chamber, because of the wedging action of lthe tapered plungerbuilding up a maximum stress at or near the outer collar face which istransmited via lateral shear stresses to the inner collar face.

Where this effect is undesirable due to plunger configuration the collarmay be so designed as to include a body of material of low yield shearand low compressive strength which while reducing the iniluance of thelateral shear stresses due to wedging described above, acts as apressure transmitting medium.

Two embodiments of dies according to the invention Y are illustrated .asFIGURES l and 2, in the accompanying drawings, both views beingsections. FIGURE 3 is a sectional view of a suitable heating means.

yIn FIGURE 1 is shown a die in which the inclusion of :a body ofmaterial of low shear strength with the collar is desirable. In thisfigure the `body 10 of the die is a ring deining a pressure chamber 12.The faces of the ring are dished at 14. The ring 10 may be made of arefractory metal-bonded carbide characterized by a very high tensilestrength and .a high compressive strength. As an example the material ofthe ring may be a medium grained tungsten carbide bonded with about 10%of cobalt.

The ring 10 as shown is supported by three high tensile steel rings 16,18, and 20 which have been shrunk or force-tted together.

Two plungers 22 have noses 24 that enter the chamber 12. The parts 26protruding from the chamber are of greater diameter than the noses.

Surrounding the parts 26 are collars 28 of steel, which may be stainlesssteel, which have annular grooves 30 that are open to the peripheralsurfaces of the plungers. Each groove 30 is iilled with la material 32having low shear strength and negligible compressibility, such as lead.The inner faces 34 of the collars adjacent to the ring are formed tocomplement or nearly to complement the dishing of the ring 10.

In use, the pressure chamber 12. is lled with charge material and thecharge die is placed between anvils 36 atached to the platens of -apress.

The outer faces 38 of the plungers 22 must be exactly complementary tothe inner faces 40 of the anvils 36; this avoids high local stresseswhere the area of contact is less than the total `area ot plunger face38. To achieve this axact complementary condition a thin layer of metalmay be introduced between the faces 38 `and the anvil face fill.

As load is applied the plunger is forced to enter the pressure chamberand the collars, being confined between the anvils and :the die ring arecompressed and eventually plastically deformed. A compressive stress isinduced in the filling 32 which is transmitted as a quasi-hydrostaticpressure to the peripheral surfaces 26 of the plungers protruding fromthe die faces.,

The part of each plunger that enters the pressure chamber 12 isobviously :smaller in diameter than the diameter of the chamber, topermit its inward movement. There are therefore annular extrusion gaps62 through which the material being compressed 4may escape. 'The widthof each gap is Vso regulated that the internal friction of the materiall eing compressed, together with the pressure developed in the filling32 is sufficient to prevent appreciable extrusion and consequent loss ofpressure. The sealing of the gaps can more eiiciently be realized byinserting into the pressure chamber 12 a body 44 of material, such aspyrophyllite, having high internal friction and deformable at thepressures involved.

The material of thebody 44 will extr'ude only to a lmited extent intothe annular gaps, being restrained by its own internal friction and thepressure within the lead. The plungers may be so designed -as to tapertoward their inner face. By this means the areas of -the annular gapsare reduced as Vthe plunger-s move inwardly into the pressure chamberand higher internal pressures are generated.

The body 44 has a central cavity 46 that accommodates the charge.

In FIGURE 2, the die ring l is the same .as in FIG- URE l, and issupported, again as in FIGURE l, by hightensi-le steel rings 1j6, 18 and20. The plungers 48 are bosses that may ormay not be inter-gral with,and project from, anvils 50' that are supported by high-tensile rings52.

The faces 54 .of the anvils flanking the plungers 48 are conical torconoidal to Vconform with or nearly to conform with the dishing of thering 10. Between the faces 54 and the ring 10= and sunrounding theprotruding portion 56 of each plunger, is a dished collarV SS of steel;for instance a medium alloy die steel `in the softened condition givingan ultimate 4tensile strength of 55 tons in 2 and an elongation ofY 20%Vmay be used. There may be linings 60 of materials, such as lead,*between the collars 58 and the plunger-s 56.

The collars, being confined between the anvils and the die ring, arecompressed and' eventually plastically deformed. Friction between thecollars and the faces of the anvils and the die ring resists thetendency to spread and there is set up an inwardly directedquasi-hydrostatic force, which is applied to the protruding parts 56 ofthe plungers and constitutes a radial support thatrincreasessubstantially the pressure which the plungers will withstand acrosstheir lateral faces.

'Friction between the collars and the anvils and the die ring may beincreased by coating the contact surfaces with jewellers rouge oranother similar high friction material.

As in the case illust-rated in FIGURE l there is an annular gap l62-between the peripheral surface of the entrant plunger and the pressurechamber wall. Extrusion of the material being compressed is restrainedby friction and the sealing effect of the collars. The width of'each gap62 is so arranged that extrusion is contained within -acceptable'limitsAs in the previous case, the seal-ing of the gaps can more eiciently berealized by inserting into the pressure chamber 12V a hollow -body 64 ofmateria-l, such as pyrophyllite having high internal lfriction anddeformable at the pressures involved. The plungers may be so ydesignedas to taper toward their inner faces. By this means lthe area oftheannular gaps 62 `are reduced as the plungers move inwardly into thepressure chamber and higher internal pressures are generated.

'I'he body 'has a central cavity 66 that accommodates the charge.

The charge may be electrically heated while it is under pressure by,-for instance, lining the cavity ofthe body 64 with a conductive tube 70that is insulated electrically from the charge by an inner tube 68.Current is fed to the tube along a path comprising a plunger 22 or 48, aconductive pad 72, also insulated electrically from the charge by a`disc 74, a second conductive pad 76 insulated electrically from thecharge by a disc 77, and the second plunger or a rigid anvil `if onlyone plunger is being used.

Alternatively, the heating element may be a conductive rod, or Wire,embedded in the charge and electrically insulated from it. Theconducting rod or wire may be of graphite. However, the charge itself,if an electrical conductor, may be used as a heating element.

In order to insulate the plungers from the body 10 of the die, aninsulating layer, such as an annular ring 78 of mica, is interposedbetween the inner face of at least one collar and the appropriate diering face. 'It is useful to coat the mica with a high friction materialsuch as jewellers rouge.

Using thedie of the invention pressures of at least the order vof 70,000atmospheres may be generated within the pressure chamber.

We claim:

1. In combination, a press and a die, between the platens of the press,having a body defining a pressure chamber, the body being dished onopposite faces, two opposed plungers movable to enter the pressurechamber rto compress a charge within it between them and supportingmeans for that part ofreach plunger that protrudes from the body, cachof such supporting means consisting in a collar surrounding lthatprotruding part and substantially complemental to the dishing of thebody, located to `be compressed between the body and a platen and madeof a material that undergoes plastic deformation at the pressure to beapplied to the die as well as being capable of exerting a sustainedinward quasi-hydrostatic pressure on the plunger periphery 2. VThesubject matter of claim 1 in which the part of the plunger that entersthe pressure chamber is diametrally less `than the protruding part.

3. The subject matter of claim 1 in which the collar is metallic. Y

4. T he subject matter of claim 3 in which the collar is of high-tensilesteel.

V5. The subject matter of claim 1 in which each collar has an annulargroove directed towards the plunger and in which the groove is iilledwith a soiid'material having low shear strength and insignificantcompressibility.

6. The subject matter of claim 5 in which the filler material is lead.

7. The subject matter of claim 1 in which the radially inner part of thecollar is of low shear strength and insignificant compressibility.

8. The subject matter of claim 7 in which the radially inner part of thecollar is of lead.

9. The subject matter of claim l including body of material within thepressure chamber hollowed to receive charge material and characterizedby high internal frictional and the ability toundergo plasticdeformation at the pressure to be applied to the die.

10. The subject matter of claim l in which the nose of each plunger issubstantially cylindrical.

References Cited in the tile of this patent UNITED STATES PATENTS2,554,499 Poulter c May 29, 19,51 2,938,998 Wilson May 31, 19602,941,241 Strong June 21, 1960 2,941,243 Bundy lune 2l, 1960 2,941,244Wentorf lune 21, 1960 2,941,246 Bundy lune 21, i196() 2,941,252Bovenkerk .Tune 2l, 1960 2,947,034 li/'eutorfY Aug. 2, 1960 '2,947,609Strong Aug. 2, 1960

1. IN COMBINATION, A PRESS AND A DIE, BETWEEN THE PLATENS OF THE PRESS, HAVING A BODY DEFINING A PRESSURE CHAMBER, THE BODY BEING DISHED ON OPPOSITE FACES, TWO OPPOSED PLUNGERS MOVABLE TO ENTER THE PRESSURE CHAMBER TO COMPRESS A CHARGE WITHIN IT BETWEEN THEM AND SUPPORTING MEANS FOR THAT PART OF EACH PLUNGER THAT PROTRUDES FROM THE BODY, EACH OF SUCH SUPPORTING MEANS CONSISTING IN A COLLAR SURROUNDING THAT PROTRUDING PART AND SUBSTANTIALLY COMPLEMENTAL TO THE DISHING OF THE BODY, LOCATED TO BE COMPRESSED BETWEEN THE BODY AND A PLATEN AND MADE OF A MATERIAL THAT UNDERGOES PLASTIC DEFORMATION AT THE PRESSURE TO BE APPLIED TO THE DIE AS WELL AS BEING CAPABLE OF EXERTING A SUSTAINED INWARD QUASI-HYDROSTATIC PRESSURE ON THE PLUNGER PERIPHERY. 